.\"-
.\" SPDX-License-Identifier: BSD-2-Clause
.\"
.\" Copyright (c) 2019 Ian Lepore <ian@freebsd.org>
.\"
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.Dd September 2, 2020
.Dt LTC430X 4
.Os
.Sh NAME
.Nm ltc430x
.Nd driver for LTC4305 and LTC4306 I2C mux chips
.Sh SYNOPSIS
To compile this driver into the kernel,
place the following line in your
kernel configuration file:
.Bd -ragged -offset indent
.Cd "device ltc430x"
.Ed
.Pp
Alternatively, to load the driver as a
module at boot time, place the following line in
.Xr loader.conf 5 :
.Bd -literal -offset indent
ltc430x_load="YES"
.Ed
.Sh DESCRIPTION
The
.Nm
driver supports the LTC4305 and LTC4306 I2C bus multiplexer (mux) chips.
It automatically connects an upstream I2C bus to one of several downstream
buses as needed when slave devices on the downstream buses initiate I/O.
More information on the automatic switching behavior is available in
.Xr iicmux 4 .
.Sh FDT CONFIGURATION
On an
.Xr fdt 4
based system, an
.Nm
device node is defined as a child node of its upstream i2c bus.
The children of the
.Nm
node are additional i2c buses, which will have their own i2c slave
devices described in their child nodes.
.Pp
The
.Nm
driver conforms to the standard
.Bk -words
.Li i2c/i2c-mux-ltc4306.txt
.Ek
bindings document, except that the following optional properties
are not currently supported and will be ignored if present:
.Bl -bullet -compact -inset -offset indent
.It
enable-gpios
.It
gpio-controller
.It
#gpio-cells
.It
ltc,downstream-accelerators-enable
.It
ltc,upstream-accelerators-enable
.El
.Pp
In addition, the following additional property is supported:
.Bl -tag -offset indent -width indent
.It Va freebsd,ctlreg2
A value to store into the chip's control register 2 during initialization.
Consult the chip datasheet for the meaning of the various bits in
the register.
.El
.Sh HINTS CONFIGURATION
On a
.Xr device.hints 5
based system, the following hints are required:
.Bl -tag -offset indent -width indent
.It Va hint.ltc430x.<unit>.at
The upstream
.Xr iicbus 4
the
.Nm
instance is attached to.
.It Va hint.ltc430x.<unit>.addr
The slave address of the
.Nm
instance on the upstream bus.
.It Va hint.ltc430x.<unit>.chip_type
The type of chip the driver is controlling.
Valid values are
.Dq ltc4305
and
.Dq ltc4306 .
.El
.Pp
The following hints are optional:
.Bl -tag -offset indent -width indent
.It Va hint.ltc430x.<unit>.ctlreg2
A value to store into the chip's control register 2 during initialization.
Consult the chip datasheet for the meaning of the various bits in
the register.
This hint is optional; when missing, the driver does not update control
register 2.
.It Va hint.ltc430x.<unit>.idle_disconnect
Whether to disconnect all downstream busses from the upstream bus when idle.
If set to zero, the most recently used downstream bus is left connected to
the upstream bus after IO completes.
Any non-zero value causes all downstream busses to be disconnected when idle.
This hint is optional; when missing, the driver behaves as if it were zero.
.El
.Pp
When configured via hints, the driver automatically adds an iicbus
instance for every downstream bus supported by the chip.
There is currently no way to indicate used versus unused downstream channels.
.Sh SEE ALSO
.Xr iicbus 4 ,
.Xr iicmux 4
.Sh HISTORY
The
.Nm
driver first appeared in
.Fx 13.0 .
